Acoustic condenser diaphragm



Oct. 13, 1931. PQTTER ACOUSTIC CONDENSER DIAPHRAGM Filed Oct. 21. 1929 Patented 9st. 13, 1931 UNITED sraras PATENT OFFICE BARB r. POTTER, or WAUKEGAN, rumors, Assrsnon T0 EPHRAIM samrme, or

r V CHICAGO, ILLINOIS ACOUSTIC connnnsnn ensign-Basra Application filed October lhis invention relates to condenser or acoustic diaphragms, and has for its object to provide an improved structure for an acoustic condenser diaphragm or likedevice. A further object is to increase the dielectric strength of a diaphragm of this class, as well as to improve its flexibility and smoothness. A further objectis to reduce the cost of a structure of this class. 7

These and other objects, as willpresently appear, are accomplished by this invention which is fully described in the following specification and shown in the accompanying drawing, in which the figure is a perspective ,15 view of a diaphragm partially cut away to illustrate the structure.

here are various uses for my invention, an examplebeing' in connection with a condenser reproducer such as is disclosed in an no application for Letters Patent of the United States, Serial No. 352,201, entitled, Acoustic condenser, filed April 3, 1929, by Philip E. Edelman, in which case my invention may be utilized in the dielectric diaphragm struc-- ture of the device therein describe In'such devices, a dielectric diaphragm consists of a flexible :thinsheet of insulating material, such, for instance, as a fabric impregnated withinsula-tion filler or oxidized linseed oil, or oil and asphaltumcompound of the class known'in the electricaltrade as, cinpirecloth, to which a coating of thin metal i il or sprayed metal finely divided inavarnish base,is attached. It has been customary, heretofore, to employ sizing, lacquer, or "varnish to cause the metal foil or finelydivided metal to adhere to the insulatingcloth. l-i hile this practice has been successful, it causes manufacturing ,=cli.tficulties, due 1 to the fact that a solvent is necessarily used inthe 1 varnish size base.

If, for example, metal foil is applied over an empire cloth surface-prepared with japan the empire cloth and dissolve or mix there- ":ed' a suitable method for making same as i'.

cloth, to which a metal foil is applied and fastened under the influence of sufficient cloth in av well :known manner.

proximately the same dielectric constant as Q" the case of a varnish adhesive material. In

1329.1 Serial No. eoisis.

with. In such case, the dielectric strength of the empire cloth. becomes weakened, dueto such dilution.

A further trouble is found in the divergent electricalcharacteristics of the adhesive varnish with r spect to the impregnated cloth, in 7 that the dielectric constant of the varnish is greater and causes unequal potential gradient distribution in the combined dielectric comprised by the empire cloth and the thin layer of varnish carried thereon. Furthermore, the varnish in slowly drying tends to somewhat stiffen the empire cloth after a time, destroying part of its desired flexibility. The trouble manifests itself in production, chiefly in the case where empire cloth is used which is slightly imperfect, or has its threads pulled with greaterthan normal spacing during manufacture. In the latter case, varnish tends to fill in the weakened portion of the cloth, but offers a different characteristic dielectric path, such that electrical rupture sometimes occurs.

The stated problem may be practically solved by a new and useful structure for-a 1 condenser dielectric, inwhich a wax having adhesive properties is employed instead of an adhesive varnish, and in ,C'OBJLHICUGH with the new product thereby afforded, I have providherein set forth. Generically I prefer-to combine with an empire cloth or varnish lIIlheat to melt the wax coating. Or I may incorporate finely divided aluminum bronze in a pot of melted wax and spray same onto'the In either case, the-melted wax tends 'to spread evenly andwhere necessary to fill in any defective areas of the insulating cloth with a good electrical insulator. having apthe empire cloth itself affords. A further advantage arises from the fact that the wax solidifies promptly-andit is not necessary to .wait fora solvent to dry out or oxidize as in 100 neral, I may use any wax for the purpose, t at is to sa any of t e known combinations of carbon, ydrogen and oxygen consisting chiefly of esters other than those of glycerine or of free fatty'acids, such for example, as beeswax, spermaceti, Chinese wax, carnauba wax, or ceresin.

I prefer to employ a wax, such as cerowax, whichhas adhesive properties as well as flexibil'ity its solid state, as it does not become brittle, or crack, but tends to improve the flexible sound deadening characteristic of soft empire cloth. Such wax further tends to improve the weather-proof characteristic of empire cloth, and preserve its operating life fet d; lon r than normal by excluding mm from t e surface of the oiled cloth.

iReferring to the illustration shown, my I d structure for the condenser dielectrio or diaphragm consists of a sheet of oiled insulatin eompound impregnated cloth or claim cfoth, which may be stretched upon 8 m (not shown) and upon one side of 'this eloth a thin layer of wax 2 is coated. while the metal foil 3 is attached to cloth 1 hymns of the adhesive wax 2. A terminal may be similarly fastened to the metal foil -3 b means of wax 2 coated on one side of the strip terminal 4, so that an electrical potential may be applied thereto. Any co-operating e e 5 may be used to complete a condenser structure. 1 The preferred manner of ap lying wax 2 to dielectric fabric 1 is to ru a piece of solid wax 2 lightly over. a heated flat iron and to rub the waxed flat iron evenly over *one side of the cloth 1, while said cloth is held stretched lightly to remove wrinkles therefrom and flat on a work table. The wax lflcqltingbecomes visible by its dull surface impen cooling; I'may also draw one surface e cloth 1 continuously and under tension we: a roller maintained in contact with a pot-f molten wax.

whepreferred manner of applying foil 3 waxed dielectric sheet 1, 2, is to lay the "inetal foil down on the waxed sheet. lay a thin sheet of fibrous material over the foil, ,and'apply a warm iron with pressure over 60 the fibrous to sheet, thereby causing the wax Qtd melt-an the foil 3 to smoothen so that when thehcat is removed the foil will be aheldmgainst the'cloth 1 by the wax 2. For continuous operation, I may employ rollers '86 in a well known manner so that a hot roller the foil against the wax coated emspiel. cloth moved with respect thereto. The

r'drawingshows the dielectric structure on an w ted scale for'purpose of illustration.

relative thicknesses, for 7 example, ter ier cloth 1, .003 to .005 inch; for wax layer-'2, .00005 to .0001 inch; and for metal foil 8, aluminum foil .0001 to .0002 inch. '1 The composite dielectric diaphragm or permanent propertiesproviding the result sou ht for, and the foil 3 adheres firmly to clot 1 under working stresses of considerable magnitude applied when the same is used in a condenser reproducer. I am aware that the said new structure has other possible uses aside from service in an acoustic condenser, such for example, as in combinations intended for regular electrical condenser service, 01' in combinations intended for weatherproofing purposes.

While I have shown and described but a few embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made which do not depart from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. An acoustic condenser diaphragm consisting of a flexible impregnated fabric insulating sheet coated with wax and a metallic surface fastened to said sheet by said wax.

2. A dielectric diaphragm consisting of empire cloth coated with wax andcarrying metal foil fastened thereto by said wax.

3. An acoustic diaphragm consistingof a dielectric impregnated fabric coated with a thin layer of insulating wax and a co-operating electrode surface therefor fastened to said fabric by said wax.

4. A dielectric diaphragm consisting of a flexible cloth impregnated with a dielectric insulator, a thin layer of adhesive wax coated on one surface of said cloth, and an electricall conductive coating attached to said cloth by said wax.

' 5. A dielectric diaphragm comprising a fabric impre nated with insulating com-' pound, and aIayer of flexible wax coated on said impregnated cloth. 1 6. An acoustic diaphragm comprising empire cloth coated with a flexible thin layer of a wax substance containing oxygen carbon, an hydrogen in the form chiefly of esters other than those of glycerine or of free fatty acids.

7. An acoustic diaphragm consisting of a thin layer of wax sandwiched between an empire cloth and metal foil in a laminated structure.

8. The method of fabricating a condenser diaphragm which consists in coating an impregnated insulating cloth with wax maintained in fluid condition by application of heat thereto.

9. The method of fabricating an acoustic condenser which consists in stretching eme influence of heat and pressure.

10. Themethod of making an acoustic condenser diaphragm which consists in applying melted wax to a sheet of empire cloth under Biro cloth, and coating wax thereon under 13 fi laminated structure thus prepared has the influence of heat and pressure, cooling said Wax, applying a layer of metal foil thereon, and fastening said foil to said cloth by means of said Wax under the further in fluence of heat and pressure.

In testimony whereof, I have hereunto set my hand this 30th day of September, 1929.

EARL F. POTTER. 

